A simple method to remove oil pollution in vacuum aluminum brazing furnace
Aluminum vacuum brazing furnace used in vacuum to obtain equipment, there is general or by popular oil equipment, such as: mechanical rotary vane pump, roots pump, oil diffusion pump, etc, although has taken some measures to prevent oil return, but it is still not completely solve the problem of return oil. According to the relevant information, diffusion pump, rotary vane pump, will return oil to the furnace. Although return oil volume is small, the brazing process of artifacts, even a short time to work simply will not have to return oil phenomenon exist, but always returns the furnace oil adsorption in the furnace temperature is not high, such as furnace lining, baffle plate, etc., accumulate over a long period, more and more. A new stove, which works for hundreds of hours, may have visible levels of oil on the reflector. Touch with your fingers, wipe with paper and cotton balls, and you can easily detect oil deposits on them. The vacuum aluminum brazing technology has high cleaning requirements on the environment and workpiece surface of the brazing furnace, and no obvious oil pollution is allowed in the furnace. As the oil volatilizes in a high vacuum environment, it may reduce the limit vacuum degree and prolong the time to reach the working vacuum degree. If the oil is not removed, the product quality will be affected and the production efficiency will be reduced. Therefore, it is a popular practice to clean the furnace regularly or irregularly. The cleaning method is usually hand scrubbing, with alcohol, acetone and other solvents, bit by bit scrubbing. Because of product oil place is mostly where no heat radiation, is also a hand or general tool is not easy to reach the place, such as multilayer reflection plate interlaminar cracks and so on, is very difficult to clean up, also must use some self-made simple tools. Even so, there are still some areas that cannot be cleaned. In our work, we gradually for a removal of vacuum aluminum brazing furnace and a simple method to oil pollution, it is used after the brazing furnace heat, using nitrogen cooling process, let the nitrogen convective circulation to conduct heat within the furnace, heating furnace in the baffle artifacts such as cold, make its temperature to 200 ℃ above, the surface adsorption of oil evaporate. This method is very effective and easy to do. The specific operation method is introduced as follows.
I. operating procedure: vacuum aluminum brazing furnace.
After the soldering process, usually nitrogen cooling general procedure is: 1, close the main valve, close the diffusion pump - 2 on rotary vane pump 2 -- 3 off before the level valve, roots pump, rotary vane pump 1 -- 4 open nitrogen charging valve to fill nitrogen furnace, for e. when the nitrogen pressure to close the nitrogen charging valve - 5 valve valve, open the fan heat exchangers and the nitrogen cycle fan, the furnace temperature quickly reduced to below 200 ℃, 6 close the nitrogen circulation fan and fan valve, heat exchanger valve open valve to restore normal pressure in the furnace - 7 -- 8 blow-in artifacts. If you want to clean up the oil in the furnace, you need to make some changes to the above nitrogen cooling procedures. First of all, after the end of brazing, the cooling water of furnace wall and furnace door is closed before starting operation. Step 1, 2, 3, 4 before operation, step 5 in the temperature reaches 400 ℃ or perform step 6: close the nitrogen circulation fan, fan and heat exchanger valves. And then let the furnace temperature natural decline until 200 ℃. Temperature of natural decline slower cooling, reduced from 400 ℃ to 200 ℃, it takes about an hour or more. Then start the rotary vane pump again. 1. Open the coarse extraction valve and take out the hot nitrogen and the evaporated oil vapor in the furnace. When the pressure drops to the point where the Cairo pump can be pumped, then the Cairo pump can be pumped again until the pressure drops below 10Pa. You can immediately perform steps 7 and 8 above, or you can keep the furnace in a thick vacuum until the next day.
Two. A few points
1. To 400 ℃ temperature quickly, in order to reduce the diffusion brazing junction silicon, is helpful to ensure the quality of joints. This is required by the aluminum brazing process and must be done.
Then take a slow, long period of natural cooling, primarily to remove the oil. At this time, due to the nitrogen in the furnace, the residual heat depends on the circulation of nitrogen, which can heat the original non-radiative adsorption of the grease cold components. The temperature of these artifacts usually only tens of degrees, in the process can rise to about 200 ℃, thus achieve the goal of the surface oil evaporation.
3. The subsequent extraction of crude vacuum, on the one hand, removes the evaporated oil vapor from the furnace chamber to prevent it from being absorbed again after cooling; on the other hand, the evaporation of oil pollution will be more thorough in the thick vacuum environment. The diffusion pump does not need to be re-opened because more than 99.99 percent of the gas in the furnace has been pumped out by the time the pressure drops to 10Pa.
4. The cooling water of furnace wall and furnace door is closed to reduce heat loss, which is more conducive to the temperature rise of furnace wall. However, because the diffuser pump and other equipment still need to be cooled, the water circulation system cannot be stopped.
After several other problems have been dealt with in this way, the oil on the reflector and some components with small thermal capacity can be basically removed. Due to the large heat capacity of the furnace wall, the cooling water was shut down in advance, but the remaining cooling water greatly increased its heat capacity, the temperature was still not high, and the effect of oil removal was the worst. Therefore, it is necessary to wash the furnace wall manually at the end. Because the oil is accumulated for a long time, the oil will stick with dust, is can't use this method to remove dust, oil pollution has been removed, the remaining dust adhesion is not strong, can use a vacuum cleaner to clean up, or use the clean compressed air to blow away. You can't clean the furnace wall first, you can do that, and when the heat evaporates in the back, you can have some oil vapor attached to it. When dust is removed, dust will stick on. So the wall of the furnace should be cleaned at the end.